US2480659A - Frequency converter - Google Patents

Description

1949- M. A. LISSMAN FREQUENCY CONVERTER Filed May 9, 1946 INVENTOR AMRCEL A. L/ss N BY Patented Aug. 30, 1949 9-.iFREQUENUSZ CONVERTER f. L Marcel A. Lissman, Cambridge, ,Mass, assignor to "'jf Raytheon Manufacturing Company, Newton, "-"'Mass., acorporation ofgDelaware .;-;-.Applicati0n May 9, 19.46;;Serial No." 668,607

' '4. Claims.

.i. 1 .Thisinventionrelateslto frequency converters,

and...mo re' particularly, .to ..aperiodic ,frequency converters iespeciallylsuitable for transforming commercial power..supp1y frequencies to higher frequencies.

" While not .limite'dithereto', the present invention admirably. adapted. for generating directly from the. raw alternating .current of commercial power lines. the'lhigh-ffrequency power utilized in induction or dielectric heating.

Apparatus either-type to which 'thepresent inventiori relates generally; comprises a plurality of oscillatory circuits having a single vfrequencydetermining network in vcommon resonant to the ,frequencyidesiredlof' the'Joutput' of the device, .fsaid oscillatory circuits including high-vacuum ..electron1 discharge' devices which, when; suitably energized" and commutatedror example, from a multi-ph'ase'. "commercial/power source; permit their respectivefioscillatorycircuits successively to functionlswhereby. said; frequency-determining network is continuously'excited at the aforesaid resonant frequency. .xExistlng; systems; "of the 'Jcharacter" just described have the disadvantage of being unable to withstand theitinverse'voltages applied "to their .electrdrr discharge devices" during the negative alternations of thelvarious-phases of their power js'upplies;:sa1d"*inversevoltages" causingisaid elec- 'tron dischargei"device's to become" damaged.

'It isftherefore, the"main object of the present 'lnventiontddesign the energizing. circuits of the electron-discharge "devices" of converter systems of the typeto' which thepresent-invention, re-

lates seas-to-protectsaid"electron discharge devices against the above referredto damage.

: lhisj-andother objects of the-=present invention; which vvill'become'moreapparent as the detailed description -thereof'progresses; are attained; briefly; in" the following manner: 5 e invention conventionally'contemplates the provision of a plurality of oscillatory circuits havinga single ---'frequency determining'network in common, said frequency-determining network beingrescmant to the frequencydesired of the output of the device:' Each such oscillatory circuit" includes high-vacuum electron-discharge devicefor kohtrollingthe operation thereof. Energy is-applied to said oscillatory'circuits from a commercialmulti' phase power source,- the number or said es'oillatory circuits corresponding to thenumber otphases of said power source. For the'purposes orthLs-specification, the inventionwill bdclescribedin-connection with a -3'-phase powersource.

The electron-discharge devices are. so successively energized andcommutated that the oscillatorycircuitrwhose. electron-discharge device instantaneously. has the most positive potential applied to the anode, thereof controls the.high-frequency oscillations.

As a result, said oscillatory l circuits. are successively brought into operation to. cause. the above' referred to .common freenemy-determining network to be continuously excited. Inasmuch as, each electron-discharge device vconducts. for only one-third of the time, ,,.greater heat dissipation is permissible, .;and

. greater output power. is therefore obtainable.

' The oscillatory circuits are self-biasing; and a single means-common to all of said oscillatory circuits, is'utilized to'obtain said biasthereby I 1 materially reducing the control electrode current which flows from that associatedwith commutatingymethods previously employed.

Preferably; said oscillatory circuits are of the ".tunedeplate;tuned=grid*type; with the commu tating voltage so: introduced into a grounded control electrodeicircuit "that it is effectively in series LWi'th the anode voltage,iwhereby the anode-cathode voltagegconsistsof the sum of the voltages applied'between. the grounded "control electrode and anode, and thegrounded control electrode and cathode: -By means ofsuch an arrangement, the commutatingvoltage-contributes to the-power output 'of the'device.

In order to protect the electron-discharge de- Vices of the various-oscillatory circuits against the inverse voltages of the-multi-phases of the power supply, the-anodes'of said electron-discharge-devices are so returned to ground, through non-linear-impedances, for example, aseous-discharge tubes, that'at no time can any of said -anodes become'negative with-respect to their corresponding cathodes.

In the accompanying:specification there shall be described, and in the annexed drawing shown,

= anillustrative-embodiment'of the frequency con- --verter of the -present-invention. It is, however, to be clearlyunders'tood-that the present invention-is not'to be limitedto the details herein shown and described forpurposes of illustration 1 only, inasmuch as changes-therein may be made I without the'exercise of invention, and within the true spirit andascop'e'of the claims hereto appended.

"In said drawing,

Fig. 1 is a circuitdiagr-am-of an aperiodic frequency converter assembled in accordance with the principles of the present invention; and

Fig. 2 shows the relationship of the voltages of 3 the three-phase power supply utilized in connection with the circuit of Fig. 1.

Referring now more in detail to the aforesaid illustrative embodiment of the present invention, with particular reference to Fig. 1 of the drawing, the numerals I0, I I and I2 generally designate high-vacuum electron-discharge devices including, respectively, cathodes I3, I4 and I5, anodes I6, I1 and I8, and control electrodes I9, 25 and 2i.

The cathodes I3, I4 and I5 of the electron-discharge devices I9, II and I2 are connected, respectively, through star-connected secondary windings 22, 23 and 24 of a three-phase power transformer 25, to ground, as at 25, and, respectively, through radio-frequency by- pass capacitors 21, 28 and 29, to ground, as at 30. Said transformer additionally includes primary windings 3!, 32 and 33 connected to the lines 34, 35 and 36 of a three-phase power source, and also another group of secondary windings 31, 38 and 39 which are star-connected, as at 39', and so disposed with respect to the secondary windings 22, 23 and 24 as to be 180 out of phase, respectively, therewith. The outer terminals of the windings 31, 38 and 39 are connected, respectively, to the anodes l6, I1 and I8 of the electron-discharge devices 19, II and I2, the conductors connecting said windings to said anodes being, preferably, threaded through a hollow, coiled conductor 49, one end of which is grounded, as at M, and the other end of which is connected to one of the plates of a capacitor 42. .By so threading the connections between the windings and anodes, the necessity for radio-frequency chokes is eliminated. The remaining plate of the capacitor 42 is grounded, as at 43, said capacitor 42 and said coiled conductor 40 constituting a tank circuit resonant to the frequency desired of the output of the device. Said tank circuit is coupled to the anodes I5, I1 and I8 of the electron discharge devices I0, II and I2, respectively, through capacitors 44, 45 and 46. When the device is'employed for dielectric heating, the plates of the capacitor 42 may receive a load 41 therebetween.

The control electrodes I9, 20 and 2I of the elec tron-discharge devices I0, II and I2 are all connected to ground, as at 48, through an inductor 49 and capacitor 59, the latter being shunted by a potentiometer 5i There is thus presented an aperiodic frequency converter which is designed to operate from a multi-phase commercial power source, and which comprises a plurality of tuned-plate, tuned-grid oscillatory circuits having a single frequency-determining network in common, said oscillatory circuits being successively operable, as will hereinafter be described, to continuously excite said frequency-determining network at the above referred to output frequency of the device.

It will be noted, however, that the electron-discharge devices I0, I I and I2 are succesively subjected to high inverse voltages, and in order to protect them against damage, the outer terminals of the star-connected secondary windings 31, 38 and 39 are connected, respectively, to the cathodes 52, 53 and 54 of gaseous-discharge tubes 55,

5B and 51,'said tubes including anodes 58,59 and duced in the secondary windings 22, 23 and 24,. but the former are intended to be of considerably greater magnitude than the latter.

I I and I2 is 500 volts.

Now, the method of commutating the oscil-- latory circuits of the present invention is suchthat the electron-discharge device having the instantaneously most positive potential applied to its anode controls the high-frequency oscillations of the device, the conducting state of said last-named electron-discharge device adjusting the bias applied to each of the electron-discharge devices in a manner similar to conventional selfbiasing oscillators having direct-current power supplies. In other words, as each electron-discharge device becomes conducting, such control electrode rectification occurs therein as to maintain the remaining electron-discharge devices in a non-conducting state, with such a negative potential on the control electrodes of said lastnamed electron-discharge devices that substantially no control electrode rectification can take place therein.

Consider the time t1, indicated in Fig. 2 of the drawing, at which the voltage across the winding 31, corresponding to phase A, is somewhat greater than one-half its positive peak, for example, 2300 volts; the voltage across the winding 38, corresponding to phase B, is somewhat less than its negative peak, for example, 4450 volts; and the voltage across the winding 39, corresponding to phase C, is somewhat less than one-half its positive peak, for example, 2200 volts, all with respect to the floating neutral point 39', which will be considered a reference point.

Under these circumstances, the cathode 52 of the gaseous-discharge tube 55 will be positive with respect to the anode 58 of said tube, and said tube will be non-conducting. The cathode 54 of the gaseous-discharge tube 51 will be positive with respect to the anode 60 of said tube, and said tube will also be non-conducting. However, the cathode 53 of the gaseous-discharge tube 55 will be negative with respect to the anode 59 of said tube, and said tube Will be conducting.

Hence, there appears upon the anode 16 of the electron-discharge device II] a voltage which is 6750 volts positive (the sum of the voltages across the windings 31 and 38) with respect to the grounded control electrode 19 of said electrondischarge device, and the latter, assuming, as will later be described, that its control electrode is at a suitable potential with respect to its cathode,

will be conducting.

There appears upon the anode I8 of the electron-discharge device I2 a voltage which is 6650 volts positive (the sum of the voltages across the windings 35 and 39) with respect to the grounded control electrode 2| of said electron-discharge device, but, as Will later be described, the potential on said control electrode is such with respect to the cathode I5 that said electron-discharge device is maintained non-conducting.

The anode I1 of the electron-discharge device I I is, by reason of the conducting state of the gaseous-discharge tube 56, at the same potential as the grounded control electrode 25, and therefore, said electron-discharge device is protected againsttheinverse voltage acrossthe winding 38,,

Now, consider the time 752, indicated in Fig, 2 oithedrawing, at which. the voltage across the winding 31, corresponding tophase A, is somewhat less than itspositive peak, for, example, 4450, 5

volts; the voltageacross the winding 38, corre spondingto phase-His somewhat less than one: half itsmegative peak, for example, 2200 volts; and the voltage across the winding 39, corresponds.

ing. to phase C, is somewhat greaterthan one-.

half its, negative peak, for example, 2300. volts, again, allwith respect to the reference. point 39,.

UndertheSe circumstances, the cathode 52. of the gaseous-discharge tube 55 will still be positive Withrespect tothe anodel58 of said tube, and said, 15,-

tubewillstill be non-conducting. The cathode. 53 of, the gaseousedischarge, tube 55 will now be positive with respect to theanode 59 ofsaid tube, and said tube will now be non-conducting. However, the cathode 54 of thegaseous-discharge tube .51 will now be negativewith respect to;the; anode 60 of said tube, and said tube will now,be conducting.

Hence, there still appears upon the anode, l6.

of, theelectron-discharge device It a voltage;

Which is 6'750.v0lts.positive (the sum of the.volt-. ages across the windings 31 and 39) with respectto the. grounded control, electrode 19 ofsaid elec; tron-discharge device, and thelatter, assuming.

that its control electrode is still ata suitable,-30.

volts positiveithe sum of the voltages acrossthe; 3.5

windings 38 and 39) with respect to the grounded? control-electrode 20 of said electron-discharge; device, but the biasing potential on said'control, electrode is such with respect to the cathode I 4 that said electron-discharge device is maintained.

non-conducting.

Theanode [801 the electron-discharge device, l2;is, by reason of the conducting state .ofthe: gaseous-discharge tube 51, at the same potential:

asthegrounded control electrode 2|, and therefore,; said electron-discharge device is protected against the inverse voltage across the winding 39.

Now,- considerthe time is, indicated in-Fig; 2' ortheqdrawing, at which the voltagelacross the winding 31,, corresponding to phase A, is somewhat less than one-half its positive peak, for 8X''- ample, 2200 volts; the voltage across the winding: 5i3,,corresponding to phase B, is somewhat greater than oneehalf its positive peak, forvexample, 2300 volts; and the voltage across the winding 39, corresponding to phase C, is somewhat less than its: negative peak, for example, 4450 volts, all withrespect to the reference point 39'.

Under these circumstances, the cathode 52 0f thegaseous-discharge tuba -55 will still be positive with respect to the anode 58 of said tube, andsaid tube will still be non-conducting. The cathode 53 of the gaseous-discharge tube 55 will still be positive with respect to the anode 59 of said tube, and said tube will still be non-conducting.

The cathode 54 of the gaseous-discharge tube 51 will still be negative with respect to the anode I of said tube, and said tube will still be conducting. Hence, therestill appears upon the anode l0 potential-with respect to its. cathode, will 13611011! conducting;

'Ilhereappearsupon the anode I! of the'elec-,

tron-discharge device H a voltage which is 6750 volts positive (the sum of the voltages across the windings-38gand39) with respect to the grounded control electrode. 20 of said electron-discharge device; but it will be assumed that the potential on said control electrodeis such with respect to, the cathode 4 that said electrondischarge device.

is; now conducting.

The-anode 1 I 8 of the electron-discharge device.

i2'is, by reason of the conducting state of thegaseousrdischarge tube 51, still at the same poten-.-. tial as, the control electrode 2!, and therefore;

said-electronedischarge device is still protected,

against the inverse voltage across the winding 39'.

The, cycle continues in such a manner that at time is, the electron-discharge device I I will still be conducting,thegaseous-discharge tube 55 will become conducting to protect the electron-disecharge device It! against the inverse voltage across; the win ding,.31, the gaseous-discharge tube 55, will'remain non-conducting, and the gaseous-'- discharge tube 5'! Willbecome non-conducting;

Attime t5, theelectron-discharge device 12 will: be conducting; the gaseous-discharge tube 55 will:

continue to conduct to protect the electron-dis charge device .I 0; and the gaseous-discharge tubes will remainnon-conducting;

Now, the; commutating voltages across the" windings-.22, 23am 24 will be explained.

Consider the time it, indicated in Fig. 2 of the drawing, and assume that the peak voltages across thewindings 3'1, 38 and 30 are 4500 volts, the.

peak voltages'across-the windings 22, 23 and 24 are 500 volts, and the radio-frequency drives on the control electrodes 15, 20 and 2! of the elec--- tron-discharge devices 20, I! and it are 500 volts.

'fihlrther-gassume'that, with the above-mentioned radioefrequency drive app-lied to the control electrode'le-oi the electron-discharge device it, andwithout commutatin voltage across the winding 22iibeingappliedrto said control electrode, the resistance, value of the effective portion of the potentiometer 5! is such that, due to control electroderectifioation in said electron discharge device 110, there-is a normal direct-current voltage drop across said eifective portion of the potentiometer of 250 volts negative. Under the forc goingconditions, when, addition to the radiofrequency drive, the commutating voltage of 500' volts is applied to the cathode is of the electrondischarge device likithe control electrode thereof will;.have'..arpositive-excursion of 250 volts, and" saidslast-narned electron-dischar e device will be come gconducting in. phase with the power supply voltage A'between the times to and is, providedtherefiective .portion'oi the potentiometer 55 is inoreasedto obtain an additional 500 volts d =ct-- current -:dropthereacross. Whllli'zth anode id of the electron-discharge deof the electron-discharge device 10 a voltage 70340-6 is going plsiiive with respect t0 the COR;

trol-electroderls thereof as a resuit the voltage which is 6650 volts positive (the sum of the .volt-. ages across the windings 31 andSd) Withrespect. to the groundedcontrol electrode IQ of said electron-discharge device, but the latter, assuming across the winding ill, the cathode i 3 of said elec It Will be noted that tron disch'arge device ldis going negative withrespect to said control electrode is as a result of that its control electrode is at a suitable biasing the out-of-phase voltage across the secondary winding 22. Thus, the anode-cathode voltage is the sum of the voltages across said windings 3'! and 22, so that the commutating voltage actually contributes to the output power of the device.

It will also be noted that at the instant t7 all control electrodes will be depressed 750 volts below ground potential, while the voltages across the secondary windings 23 and 24 will be 250 volts positive with respect to ground. As a result, biasing voltages Will be applied to the control electrodes 20 and 2! of the electron-discharge devices ll and i2 amounting to 1000 volt negative with respect to the cathodes I 4 and 95 thereof. Hence, the latter two electron-discharge devices, when energized by the 500 volts radio-frequency drive, will still be biased 500 volts negative, more than enough to maintain them in a non-conducting state and prevent them from drawing control electrode current.

When the time it is reached, commutation takes place, the electron-discharge device H takes over control of the circuit, and the devices l8 and I2 are maintained non-conducting. Finally, when the time no is reached, commutation again takes place, and between said time 1310 and time tn, the electron-discharge device l2 conducts, and maintains the devices ii! and H in a non conducting state.

While particular voltage values have been assumed in the foregoing explanation, it is to be clearly understood that these values are merely illustrative, and the components of the device may be adjusted to obtain an other values which will result in commutation of the character described. It is to be further understood that while tuned-plate, tuned-grid oscillators have been discussed herein, any other type of oscillator, or other electrical circuit, will function as well.

This completes the description of the aforesaid illustrative embodiment of the present invention. It will be noted from all of the foregoing that the present invention provides a simple and efiicient device for converting commercial power frequencies to higher frequencies. It will further be noted that the device operates under conditions of efficiency, stability and regulation comparable to those of a conventional self-biasing oscillator having a direct-current power supply. It will be still further noted that control electrode rectification in the oscillation-controlling electron-discharge device alone controls the biasing of the remaining electron-discharge devices, and each electron-discharge device, during the periods that it is intended to be non-conducting, is protected against the inverse voltages of the variou phases of the power supply.

Other objects and advantages of the present invention will readily occur to those skilled in the art to which the same relates.

What is claimed is:

1. In combination with an electrical circuit including a plurality of electron-discharge devices each of which has a cathode, a control electrode and an anode: means, adapted to be energized from a multiphase, alternating-current power supply, for applying such potential differences between the anodes and cathodes, and the control electrodes and cathodes of said electron-discharge devices as to render the same successively conducting; and a switching device connected across each of said electron-discharge devices, whereby 7 the anodes of said electron-discharge devices are prevented from going negative wtih respect to their corresponding cathodes during the negative alternations of said power-supply phases,

2. In combination with an electrical circuit including a plurality of electron-discharge devices each of which has a cathode, a control electrode and an anode: means, adapted to be energized from a multi-phase, alternating-current power supply, for applying such potential differences between the anodes and the cathodes, and the control electrodes and cathodes of said electrondischarge devices as to render the same successively conducting; and a gaseous-discharge tube inversely connected across each of said electrondischarge devices, whereby the anodes of said electron-discharge devices are prevented from going negative with respect to their corresponding cathodes during the negative alternations of said power-supply phases.

3. An aperiodic frequency converter comprising: a plurality of oscillatory circuits having a single frequency-determining network in common, said frequency-determining network being resonant to the frequency desired of the output of said converter; each of said oscillatory circuits including an electron-discharge device having a cathode, an anode, and a control electrode; means, adapted to be energized from a multiphase, alternating-current power supply of a frequency different than that desired of the output of said converter, for applying such potential differences between the anodes and cathodes, and

the control electrodes and cathodes of said electron-discharge devices as to render the same successively conducting; and a switching device connected across each of said electron-discharge devices, whereby the anodes of said electron-discharge devices are prevented from going negative with respect to their corresponding cathodes during the negative alternations of said powersupply phases.

4. An aperiodic frequency converter comprising: a plurality of oscillatory circuits having a single frequency-determining network in common, said frequency determining network being resonant to the frequency desired of the output of said converter; each of said oscillatory circuits including an electron-discharge device having a cathode, an anode, and a control electrode; means, adapted to be energized from a multiphase, alternating-current power supply of a frequency different than that desired of the output of said converter, for applying such potential differences between the anodes and cathodes, and the control electrodes and cathodes of said electron-discharge devices as to render the same successively conducting; and a gaseous-discharge tube inversely connected across each of said electron-discharge devices, whereby the anodes of said electron-discharge devices are prevented from going negative with respect to their corresponding cathodes during the negative alternations of said power-supply phases.

MARCEL A. LISSMAN.

REFERENCES QITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 0 Number Name Date 1,224,689 Thomas May 1, 1917 2,319,072 McArthur May 11, 1943

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